You need BES. Nothing else will do it. No hack of any kind will allow it. BES or nothing. BES Express is free for the first user, $109 each additional user, and if you are lucky, and buying 5 blackberries soon, you can get 5 users for free.

Is BES Express for non-corporate sever environment, e.g., can it be set up on a home computer to obtain this functionality with accept/decline appts?